Former England and Tottenham striker Jimmy Greaves is in intensive care after suffering a severe stroke on Sunday.
A statement from Greaves' family confirmed that the 75-year-old had been taken ill, having recovered from a minor stroke in 2012.
Greaves scored 44 goals in 57 England games, the fourth-highest total of all time.
He also scored 266 goals in 379 matches for Spurs.
A statement issued on behalf of Greaves' family read: "Football legend Jimmy Greaves suffered a severe stroke on Sunday May 3, and is in intensive care in hospital.
"His wife, Irene, and four children have asked for privacy during what is a worrying time for the family.
"They will issue a bulletin on his condition when it is appropriate.
"England's greatest ever goal scorer was 75 on February 20, and has been working regularly on the personal appearances circuit in harness with his friend and agent Terry Baker.
"Jimmy had a minor stroke in 2012, but appeared to have made a full recovery. He was due to be inducted into the Tottenham Hotspur Hall of Fame on May 13 at a sell-out ceremony at White Hart Lane.
"This is all we wish to say at the present time."
Greaves is due to be inducted into the Spurs Hall of Fame a week on Wednesday.
The 75-year-old spent nine seasons at Tottenham during one of the most successful periods of the club's history.
Greaves scored the opening goal in Tottenham's FA Cup final victory over Burnley in 1962 and he also found the net in European Cup Winners' Cup final against Atletico Madrid, which the London club won 5-1.
Greaves started his career at Chelsea, where he broke into the first-team squad after scoring 114 goals for the youth team.
Once he had been promoted to the seniors, he scored a 132 goals in 169 games.
Greaves then spent an unhappy six months at AC Milan before returning to London to join Spurs.
After nine years at Tottenham he moved across the capital to West Ham before seeing out his career lower down the leagues following a battle with alcoholism.
After retiring from the game, Greaves co-hosted the popular Saturday lunchtime football show Saint and Greavsie alongside former Liverpool forward Ian St John.
Tottenham posted a message of support on their official Twitter feed shortly after the news of Greaves' stroke emerged.
"Everyone at the club wishes Jimmy Greaves a speedy recovery after he suffered a stroke yesterday," the message read.
"Our thoughts are with Jimmy and his family at this difficult time."